Potable water reservoirs such as standpipes (normally tanks with height greater than diameter), ground storage tanks (normally tanks with height less than diameter) or elevated storage tanks are connected to water distribution systems and are used, among other things, to supply water to the systems and/or maintain the pressure in the systems during periods when water consumption from the system is higher than the supply mechanism (pumps or pumping stations) to the system can provide. The reservoirs are therefore usually filling during periods when the system has supply capacity that exceeds the current consumption demand on the system or discharging into the system when the system has supply capacity that is less than the current consumption demand on the system. Potable water reservoirs typically contain water which has been treated through the addition of a disinfectant to prevent microbial growth in the water. Disinfectant concentrations in stored water decrease over time at a rate dependant upon a number of factors such as temperature, cleanliness of the system etc. This can result in unacceptable water quality if the period of retention of the water, or any part thereof in a reservoir, becomes too long or if the incoming fresh, treated water is not properly mixed with the existing stored water in a reservoir. Therefore, the age or retention period of water within potable water reservoirs and the mixing of incoming fresh water with the existing water are of concern to ensure that the quality of the water will meet the regulatory requirements for disinfectant concentrations. In addition, during periods of below freezing weather, the top surface of the water will cool and may freeze (this is referred to as an ice cap) unless it is exchanged for or mixed with the warmer water entering the reservoir. An ice cap may adhere to the reservoir walls and become thick enough to span the entire surface even when the water is drained from below. If sufficient water is drained from below a fully spanning ice cap, a vacuum is created, collapsing the ice cap which in turn can create, during the collapse, a second vacuum which can be much larger than the reservoir venting capacity and can result in an implosion of the roof and possibly the upper walls of the reservoir.
Water reservoirs are often filled and drained from a single pipe or a plurality of pipes located at or near the bottom of the reservoir. Under these conditions, when fresh water is added to the reservoir, it enters the lower part of the reservoir and when there is demand for water in the system, it is removed from the lower part of the reservoir resulting in a tendency for the last water added to be the first to be removed. This can be referred to as short circuiting. Temperature differences between stored water and new water may cause stratification which can in turn exacerbate short circuiting and water aging problems. Filling and draining from a single or a plurality of pipes located at or near the bottom creates little turbulence particularly in areas within the reservoir remote from these inlet and outlet pipes. As a result, the age or residency time of some waters within parts of the reservoir can be very long, resulting in loss of disinfectant residual, increase in disinfection by-products, biological growth, nitrification and other water quality and/or regulatory issues. This is referred to herein as “stagnation” or “stagnant water”. A perfect system would provide a first in, last out scenario (“cycling”), however, perfect cycling is either not possible or is cost prohibitive. A preferred system provides a tendency toward cycling combined with a first mixing of the new water with existing tank contents that are most remote from the point of withdrawal. A preferred system would efficiently mix new water entering the tank with the existing tank contents thereby preventing stagnation. A preferred system would provide total mixing of the new water with the existing tank contents in the shortest period of time. A preferred system would reduce the water age or residency time and related problems. A preferred system would eliminate the potential for ice cap formation. A preferred system would use the energy of the water entering and exiting the reservoir to perform all of the mixing functions. A preferred system would be adaptable to both of the two common types of reservoirs: i) reservoirs having separate inlet and outlet pipes which fill the reservoir through one pipe or a plurality of ports on one pipe (inlet) and drain the reservoir through a separate pipe or a plurality of ports on a separate pipe (outlet), said inlet and outlet pipes being remotely valved and remotely connected or remaining separate; and ii) reservoirs having a common inlet/outlet pipe which fills the reservoir and drains the reservoir through a common or singular pipe, manifold or header.
Prior art exists which attempts to promote mixing in reservoirs through a variety of systems and methods, all of which to varying degrees are inefficient or ineffective. These proposed systems and methods, and their deficiencies, include the following:                a) The introduction of water into a reservoir through plain end inlet pipe(s) which are remotely spaced either horizontally or vertically from the outlet pipe(s) and the reliance on the physical separation only of the inlet and outlet pipes to accomplish mixing. Due to the fact that the preponderance of reservoirs fill at a very low rate of flow, this method introduces the water gently into the reservoir, does not encourage mixing throughout the reservoir, allows short circuiting of the water between the inlet and outlet locations and results in zones of stagnant water (dead zones).        b) The introduction of water into a reservoir 1) through holes in inlet pipes or manifolds, 2) through tees in inlet pipes or manifolds, and 3) through either of the preceding equipped with reducers, duckbill check valves or a combination of the two to increase the velocity of the incoming water. All of these methods create a hydraulically chaotic introduction of the fresh water resulting in an almost immediate mixing with the existing water in close proximity only and creating little effect on areas remote from the points of introduction.        c) The introduction of water into a reservoir via a singular or a plurality of inlet and outlet pipes or ports, remote from each other oriented roughly in the same plane or elevation, often at or near the bottom of the reservoir, using the inlet ports similar to or as outlined in (b) above. These piping arrangements are typically ineffective or inefficient in that the water is not introduced properly as noted in (b) and tends to short circuit or flow directly from the inlet to the outlet, thus being unable to eliminate dead zones that occur in the reservoir.        d) The introduction of water into a reservoir via a singular inlet riser preceded by a reducer. This piping arrangement, due to the length of the inlet pipe following the reducer, fails to develop the characteristics of a jet flow and results in the mixing or lack of mixing as defined in (a) above.        e) The introduction of water into a reservoir via a singular or a plurality of inlet and outlet pipes or ports, remote from each other oriented roughly in perpendicular parallel planes or planes at 90 degrees to each other using the inlet ports similar to or as outlined in (b). These piping arrangements also are typically ineffective or inefficient in that the water is not introduced properly as noted in (b) and tends to short circuit vertically or flow directly from the inlet to the outlet thus being unable to eliminate dead zones that occur in the reservoir.        
A deficiency of prior art systems and methods in general is the failure of the prior art to address the necessity of positioning and configuring the outlet pipes so as to discourage any tendency toward short circuiting and encourage a broad and general withdrawal of fluid across the full horizontal area of the reservoir or, when applicable, a vertical area.
It is desirable to provide an inexpensive and easily maintained mixing system for use in reservoirs in order to reduce the potential for dead zones, stagnation and excessive aging of the contained water and further to reduce the potential for the formation of dangerous ice caps.